One of the biggest natural features in Illinois is the Rock River. This stretch of water reaches about 285 miles in length and connects with the Mississippi River. The merging spot of the two rivers can be found in Rock Island. The river runs through five different counties, including Lee, Ogle, Rock Island, Whiteside and Winnebago. If you’re interested in viewing the Rock River for yourself, you can visit the following Northwestern Illinois locales:OregonByronRockfordSouth BeloitRocktonRoscoeMachesney ParkLoves ParkGrand DetourDixonSterlingRock FallsLyndonProphetstown